Introduction

The term tight gas sands refers to low permeability sandstone reservoirs that produce primarily dry natural gas. A tight gas reservoir is one that cannot be produced at economic flow rates or recover economic volumes of gas unless the well is stimulated by a large hydraulic fracture treatment and/or produced using horizontal wellbores (Holditch, 2006). This definition also applies to coalbed methane, shale gas, and tight carbonate reservoirs.

History

The development of many tight gas sand fields that are productive today began in the 1970s. These include fields in East Texas (Dew-Mimms Creek), the Piceance Basin of northwestern Colorado (Rulison, Mamm Creek), the Green River Basin of Wyoming (Jonah, Pinedale, Wamsutter), and the Denver-Julesberg Basin of Colorado (Wattenberg). Early development consisted of widely-spaced wells producing at low rates. Drilling accelerated in the 1980s due, in part, to tax credits that encouraged the development of low permeability (less than 0.1 millidarcy) reservoirs. By the 1990s, advances in 3-D seismic, horizontal drilling, and hydraulic fracture stimulation allowed wells to be placed and completed more effectively, increasing their rates and reserves. In the 2000s, rising gas prices coupled with large investments by growing companies drove-up rig counts and resulted in tens of thousands of wells being drilled.

Resources

Tight sands produce about 6 trillion cubic feet (TCF) of gas per year in the United States which is 25% of the total gas produced. As of January, 2009, the U. S. Energy Information Administration (EIA) estimates that 310 TCF of technically recoverable tight gas exists within the U.S, representing over 17% of the total recoverable gas. Worldwide, more than 7,400 TCF of natural gas is estimated to be contained within tight sands (Rogner, 2006) with some estimates as large as 30,000 TCF.

Challenge

Developing this gas will be a huge challenge to geoscientists faced with understanding the depositional setting, stratigraphy, structure, geochemistry, geomechanics, seismic character, and petrophysical properties controlling production. Some of the greatest challenges include (1) understanding how and where these rocks are charged with gas, (2) what controls the location of highly-productive “sweetspots”, and (3) what factors, such as sandbody size and heterogeneity, account for the large variations in well drainage areas.

For a complete version of the above, see the Committee’s Annual Report (May 2013) on the EMD Members Only page (log-in required).

If you would like to learn more about tight gas sands or to receive information on tight gas sands, or on activities of the EMD Tight Gas Sands Committee, join the EMD. If you are already an EMD Member, see “Members Only Page” http://emd.aapg.org/members_only/tightgas/index.cfm for updates on tight gas sands, for links to technical information on tight gas sands, and for related environmental information that may impact tight gas sands.